1. Field of the Invention
This invention relates to wind turbine apparatus and, more particularly, to air foil sail apparatus for wind turbines.
2. Description of the Prior Art
U.S. Pat. No. 155,472 discloses a wind turbine having a horizontal axis of rotation and a control system which employs a movable weight. The movement of the weight causes the pitch of the sails to vary such that the speed of rotation is diminished as the force of the wind increases. This provides a regulatory system or control system for holding the speed of rotation relatively constant even though the velocity of the wind varies substantially.
U.S. Pat. No. 215,035 discloses another type of wind turbine having a vertical axis of rotation and vanes or sails that are expanded or contracted in accordance with the wind speed through a control system which includes a coil spring. The sails or buckets are secured to fixed or rigid top and bottom elements which move towards and away from each other in response to wind speed and the force of the coil spring. The greater the wind velocity, the closer the top and bottom elements of the sails or buckets are together, thus diminishing the area of the sails available to the wind. Conversely, as the wind velocity diminishes, a greater area of the sails is available to the wind by the movement of the structural elements.
U.S. Pat. No. 227,842 discloses a weight system connected to vanes that control the pitch of the vanes in response to the speed of the wind. The apparatus includes a vertical axis of rotation, with the weights moving vertically in response to the speed of rotation of the apparatus.
U.S. Pat. No. 243,169 discloses a horizontally rotating element having flexible sails. The sails are triangular in configuration, with one edge of the sails relatively fixed and a corner of the sails secured to a weight system which allows the sails to spill wind when the rotation speed increases due to increased wind velocity and, when the wind velocity decreases, allows the weight to move to increase the area of the sails available to catch the wind.
U.S. Pat. No. 1,804,493 discloses another vertical axis of rotation wind turbine which includes tension springs and weights. The combination of the springs and weights causes the sails to furl as the wind speed increases. As the wind speed decreases, the tension spring and the weights cause the sails to unfurl, thus allowing greater sail area to be available to the wind.
U.S. Pat. No. 2,015,777 discloses a horizontal axis of rotation using triangular shaped sails and tension springs. As wind speed increases, the tension springs stretch and the vanes flatten out so as to decrease the area of the sails or vanes available to the wind. As the wind speed decreases, the sails or vanes are pulled by the tension springs to provide a greater frontal area available to the wind.
U.S. Pat. No. 4,191,507 discloses another type of wind turbine having a vertical axis of rotation and a plurality of sails. The sails have a fixed edge and a flexible edge. When the fixed edge is the trailing edge, the sails are available to the wind, but when the fixed edge is the leading edge to the wind, the sails flatten out to decrease the drag. The apparatus is designed for minimizing drag in a lightweight windmill.
All of the above noted patents are of the drag type. Some of the above noted patents have horizontal axes of rotation and some have vertical axes of rotation. In general, vertical axis rotors have a major advantage over horizontal axis rotors in that they do not have to be turned into the wind as the direction of the wind changes. This simplifies the design requirements of the system and at the same time decreases or eliminates certain forces which may cause more stress on blades, bearings, and other elements or components of horizontal axis systems.
Vertical axis drag devices of the prior art generally have relatively high starting torques, but they also usually have relatively low tip-to-wind speeds and relatively low power outputs per given rotor size and weight.
With rotors utilizing aerodynamic configurations to provide lift force, relatively high tip-to-wind speeds and accordingly relatively high power outputs per given rotor size, etc., are provided. However, the control systems for varying the rotational speed of the rotors includes the control of the pitch of the particular blade or air foil. For drag devices, the control systems generally include apparatus for controlling the size of the drag device, usually a sail, that is available to the wind. In general, as the wind speed increases, the size of the sail decreases, and vice-versa, to provide a relatively constant rotational speed. The above-discussed patents disclose several different types of control systems.
As is well known and understood, the greater the diameter of the rotor, the slower the revolutions per minute may be to provide a relatively high tip speed. In the apparatus of the present invention, the diameter of the rotor may be virtually any size, depending on the land available, the terrain, and other factors.